System and environment
In the study of thermodynamics, a major branch of chemistry and physics, the concepts of "system" and "surroundings" are fundamental. These terms help us understand how energy and matter interact in different scenarios and provide a framework for explaining various processes observed in nature.
What is the system?
The "system" in thermodynamics refers to the part of the universe that is being studied, observed, or focused on. The boundaries of the system can be real or imaginary and range from a single atom to an entire galaxy.
Systems can be classified into three main types:
- Open system: An open system can exchange both energy and matter with its surroundings. A classic example of an open system is a pot of boiling water. Water molecules (matter) can escape from the pot as steam, and heat (energy) is constantly being exchanged between the pot and the surrounding air.
- Closed system: A closed system can only exchange energy, not matter, with its surroundings. Imagine a closed container of gas from which no gas can escape. However, heat can still be exchanged with the environment.
- Isolated system: An isolated system does not exchange energy or matter with its surroundings. It is completely self-contained. An ideal thermos bottle is an example of this, although true isolation is practically impossible because some energy exchange will always occur.
Representation of systems
To help you visualize, for any process or experiment imagine dividing the universe into two parts: the "system" and the "surroundings." Below is a simple illustration:
,
| Environment |
,
| | System | |
,
,
Understanding the environment
The term "surroundings" in thermodynamics refers to everything outside the system. The surroundings provide or absorb the energy or matter that is exchanged with the system. When we write equations or measure changes, they are relative to this surrounding environment.
For example, if we consider a beaker inside which a chemical reaction is taking place, the beaker and its contents represent the system, while the air in the laboratory can be considered the surroundings. Heat, light or any other form of energy released or absorbed during the reaction will be exchanged with these surroundings.
Examples and visualizations
Boiling water - open system
Consider a pot of water boiling on the stove. The water and its steam together form the system. Heat from the stove conducts through the pot to the water, and the water steam escapes into the air. Both matter (water vapor) and energy (heat) are exchanged with the surrounding environment:
,
| Environment |
| (air and heat source) |
,
| | Boiling water | |
,
,
Sealed container - closed system
Imagine a sealed container full of gas submerged in a tub of water. The gas inside the container is the system. While no gas flows out or in, energy in the form of heat can pass through the walls of the container. Therefore, this is a closed system:
,
|Water Bath (Around)|
,
| | Sealed Gas Container| |
,
,
Thermos flask - the ideal isolated system
In a thermos flask designed to minimize thermal exchange, the hot or cold liquid inside the flask is the only system. Ideally, no heat or substance moves in or out, although in reality, some heat can still be lost. The flask represents an isolated system:
,
| (Ambient) |
,
| | Thermos with liquid | |
,
,
Interaction between the system and the environment
In thermodynamics, we are interested in how systems exchange energy with their surroundings. This is done primarily through heat and work:
- Heat (q): Energy transfer due to temperature difference between the system and surroundings.
- Work (w): Energy is transferred when an external force does work on a system, such as lifting a weight or compressing a gas.
The basic energy equation used to describe these interactions in thermodynamics is the first law of thermodynamics, often expressed as:
ΔU = q + w
where ΔU is the change in internal energy of the system, q is the heat exchanged, and w is the work done on or by the system.
Examples of energy transfer
Example 1: Heating a gas in a cylinder
Imagine a cylinder with a moving piston containing a gas, which we will consider as the system. When you heat the gas, it expands and does work by pushing the piston, meaning it transfers energy to its surroundings:
,
The piston moved up
gas in cylinder
, (task completed)
,
The added heat (q) increases the energy of the gas, and as the gas expands, it does work (w) on the piston.
Example 2: Chilling a beverage in a glass
The beverage in the glass is the system, while the ambient air is the surroundings. When it is placed in a refrigerator, heat is released from the beverage to the surroundings until thermal equilibrium is reached. Here, heat transfer is the exchange of energy between the system and the surroundings.
Conclusion
Understanding the concepts of system and surroundings is essential in thermodynamics because it helps analyze energy transformations. Whether studying a chemical reaction, a physical transformation, or a thermodynamic process, defining the system and its interaction with the surroundings allows scientists to effectively use the laws of thermodynamics.
Thermodynamics not only helps us understand the natural world, but is also of tremendous use in understanding engines, refrigerators, and even biological processes. The clear distinction between the system and the surroundings helps to accurately calculate energy transformations, opening up many scientific and engineering possibilities.
Comments